Resumen de Estudio de pequeños elementos magnéticos en la fotosfera y cromosfera solar con telescopios en tierra y espaciales.
The photosphere is the best known layer of the Sun, as it delimits its surface and furthermore, it has been observed in detail since the beginning of the telescopic era. The convection zone redistributes the magnetic field over the photosphere and the upper layers. On the many scales of the solar surface magnetism, the smallest elements seen in the photosphere are the most unknown, due to the limit in resolution of a finite telescope. The structures that are smaller than typically 100 km are smeared out. In this Thesis, the small bright features of the magnetic network and internetwork over the resolution limit are analysed from the dynamical point of view, and linked with their physical properties as the magnetic field and intensity.
The instruments used in this text for data acquisition are the Swedish Solar Telescope, the spatial telescope HINODE and the balloon-borne solar telescope Sunrise. From this suite of instruments, the disk centre of the Sun have been explored with the aim of studying these smallest blocks of the solar magnetism. Magnetic field densities have been estimated by inversions, weak-field approximation and center-of-gravity method.
The observatory Sunrise and its magnetograph IMaX, completed its first flight on 2009, from June 8 to June 13. It acquired high-quality data on the Stokes parameters I,Q,U,V from where different physical parameters, namely the line-of-sight velocity, longitudinal and transverse magnetic field density and line minimum can be extracted. In this Thesis, the data mining of 2009 June 10 and 11 is carried out, and all the subsequent reduction, such as the flat-field correction, spectral line removal, dark current correction, and image restoration by the Phase Diversity method. The data products are available to the scientific community for public use.
One of the results of this Thesis is a multi-wavelength description of a vortex-like flow. The small magnetic features are bright in CN, Ca II H and G-band (from HINODE and the Swedish Solar Telescope) that correspond to a magnetic region, studied in Mg i magnetograms. The vortex-like flow is traced by magnetic centroids and divergence, where the turning motion in a downdraft is noticeable. The downdrafts are also confirmed by spectropolarimetric data, which not only allow us to estimate the magnetic field vector, but also the line-of-sight velocity. These magnetic structures evolve along ~1 hour and convective collapses can occur in the magnetic areas, having some minutes of duration. The signatures of the magnetic intensification, such large downflows and abnormal Stokes V profiles, are found in the bright points.
The study of photospheric flows is significant for many parts of this Thesis: methods like the Local Correlation Tracking allows us to analyse the development of flows, to estimate magnitudes as the divergence and vorticity on a field of view, or to inspect the interaction of flows and different magnetic structures. We examine with different time averages and correlation window sizes of the Local Correlation Tracking, the divergence and vorticity along a given field of view observed by IMaX/Sunrise on 2009, June 9. We also examined the effects of magnetogram thresholding on the calculation of divergence and vorticity. Again, the Local Correlation Tracking method allows us to study small vortex-like flows, and comparing them with another techniques: the passive advected tracers, the zero-velocity computation, and the study of the vorticity by decomposing the horizontal velocity field in two components.
The magnetic features in the photosphere are not only bright points located in the intergranular lanes. We have investigated flux emergence processes in two large exploding granules with IMaX/Sunrise data. These granules reach mesogranular sizes (5-8 Mm). The typical expansion velocity of the granules is 0.6 km/s and 1 km/s for the magnetic patches that cover the mesogranular-sized granules. Divergence maps confirm the mesogranular scale. Some magnetic loops, featured as two opposite polarity patches linked by a transverse field magnetic patch are detected in the field of view. These magnetic field emergence cases are compared to magnetohydrodynamic simulation in continuum and longitudinal magnetic field, yielding to similar results.
